+48. Seventh Experiment.+--I also examined the behaviour of fire-air with sulphur (§ 23). As soon as the burning sulphur came into contact with the fire-air contained in the flask, the flame became much larger and brighter. When this fire had gone out, the water in the dish had found a way to come through the mass into the flask, which became 3/4 filled with it. As I employed for these last 3 experiments a flask which was only of 30 ounces measure, I was obliged to arrange the stand (§ 21) to suit. +49.+ I have mentioned (§ 16) that I found vitiated air lighter than ordinary air. Must it not follow from this that the fire-air is heavier than our air? As a matter of fact, I actually found, when I accurately weighed as much fire-air as occupied the space of 20 ounces of water, that this was almost 2 grains heavier than the same bulk of common air. +50.+ These experiments shew, therefore, that this fire-air is just that air by means of which fire burns in common air; only it is there mixed with a kind of air which seems to possess no attraction at all for the inflammable substance, and this it is which places some hindrance in the way of the otherwise rapid and violent inflammation. And in fact, if air consisted of nothing but fire-air, water would surely render small service in extinguishing outbreaks of fire. Aerial acid mixed with this fire-air, has the same effect as vitiated air. I mixed one part of fire-air with 4 parts of aerial acid; in this mixture a candle still burned moderately well. The heat which lurks in the small interstices of the inflammable substance cannot possibly make up so much heat as is felt in fire; and I think I am not mistaken when I conclude from my experiments that the heat is really brought forth and produced in the first place from fire-air and the phlogiston of the inflammable substance.... * * * * *